Precursors for CVD silicon carbo-nitride films

ABSTRACT

Classes of liquid aminosilanes have been found which allow for the production of silicon carbo-nitride films of the general formula Si x C y N z . These aminosilanes, in contrast, to some of the precursors employed heretofore, are liquid at room temperature and pressure allowing for convenient handling. In addition, the invention relates to a process for producing such films. 
     The classes of compounds are generally represented by the formulas: 
     
       
         
         
             
             
         
       
         
         
           
             and mixtures thereof, wherein R and R 1  in the formulas represent aliphatic groups typically having from 2 to about 10 carbon atoms, e.g., alkyl, cycloalkyl with R and R 1  in formula A also being combinable into a cyclic group, and R 2  representing a single bond, (CH 2 ) n , a ring, or SiH 2 .

CROSS REFERENCE TO RELATED APPLICATION

The present patent application is a continuation application of U.S.patent application Ser. No. 12/267,790 filed Nov. 10, 2008, now issuedU.S. Pat. No. 7,932,413, which is a divisional application of U.S.patent application Ser. No. 11/129,862 filed May 16, 2005, now issuedU.S. Pat. No. 7,875,556.

BACKGROUND OF THE INVENTION

In the fabrication of semiconductor devices, a thin passive layer of achemically inert dielectric material such as, silicon nitride (Si₃N₄) orsilicon carbo-nitride (Si_(x)C_(y)N_(z)) is essential. Thin layers ofsilicon nitride function as diffusion masks, oxidation barriers, trenchisolation, intermetallic dielectric material with high dielectricbreakdown voltages and passivation layers. Many applications for siliconnitride coatings in the fabrication of semiconductor devices arereported elsewhere, see Semiconductor and Process technology handbook,edited by Gary E. McGuire, Noyes Publication, New Jersey, (1988), pp289-301; and Silicon Processing for the VLSI ERA, Wolf, Stanley, andTalbert, Richard N., Lattice Press, Sunset Beach, Calif. (1990), pp20-22, 327-330.

Many of the new semiconductor devices require dielectric films that havevery low etch rates or very high film stresses, or both. It is alsopreferred, and sometimes necessary, that the films be formed attemperatures below 600° C. while maintaining good electricalcharacteristics. Film hardness is another factor to consider in thedesign of the electrical components and the silicon nitride films dooffer extremely hard films.

One of the commercial methods for forming silicon nitride coatingsemploys dichlorosilane and ammonia as the precursor reactants. Lowpressure chemical vapor deposition (LPCVD) using precursors such asdichlorosilane and ammonia require high deposition temperatures to getthe best film properties. For example, temperatures greater than 750° C.may be required to obtain reasonable growth rates and uniformities.Other processing issues involve the hazardous aspects of chlorine andchlorine byproducts.

The following articles and patents are cited as representative of theart with respect to the synthesis of organosilanes and depositionprocesses employed in the electronics industry.

A. K. Hochberg and D. L. O'Meara, Diethylsilane as a Silicon Source forthe Deposition of Silicon Nitride and Silicon Oxynitride Films By LPCVD,Mat. Res. Soc. Symp. Proc., Vol. 204, (1991), pp 509-514, disclose theformation of silicon nitride and silicon oxynitride films usingdiethylsilane with ammonia and nitric oxide by LPCVD. The deposition iscarried out in a temperature range of 650° C. to 700° C. The depositionis limited generally to a temperature of 650° C. as the deposition ratedrops to below 4 ANG./min at lower temperatures.

Sorita et al., Mass Spectrometric and Kinetic Study of Low-PressureChemical Vapor Deposition of Si ₃ N ₄ Thin Films From SiH ₂ Cl ₂ and NH₃, J. Electro. Chem. Soc., Vol. 141, No. 12, (1994), pp 3505-3511,describe the deposition of silicon nitride using dichlorosilane andammonia using a LPCVD process. The formation of ammonium chloride leadsto particle formation and deposition of ammonium chloride at the backendof the tube and in the plumbing lines and the pumping system.

Aylett and Emsley, The Preparation and Properties of Dimethylamino andDiethylamino Silane, J. Chem. Soc. (A) p 652-655, 1967, disclose thepreparation of dimethylamino and diethylaminosilane by the reaction ofiodosilane with the respective dialkyl amine.

Anderson and Rankin, Isopropyldisilylamine and Disilyl-t-butylamine:Preparation, Spectroscopic Properties, and Molecular Structure in theGas Phase, Determined by Electron Diffraction, J. Chem. Soc. DaltonTrans., p 779-783 1989 disclose the synthesis of disilyl amines of theformula NR(SiH₃)₂, e.g., isopropyldisilylamine and disilyl-t-butylamineand they provide spectroscopic comparisons to the correspondingmethyldisilylamine.

Japanese Patent 6-132284 describes the formation of silicon nitridefilms using organosilanes having a general formula (R₁R₂N)_(n)SiH_(4-n),(where R₁ and R₂ range from H—CH₃—, C₂H₅—C₃H₇—, C₄H₉—) by either aplasma enhanced chemical vapor deposition or thermal chemical vapordeposition in the presence of ammonia or nitrogen.

U.S. Pat. No. 5,234,869 discloses the formation of a silicon nitridefilm by CVD using Si(N(CH₃)₂)₄ and ammonia as reactant gases. A chambertemperature of 700° C. and a pressure of 0.5 Torr was used for thedeposition. Other reactants selected from the group consisting ofSiH(N(CH₃)₂)₃, SiH₂(N(CH₃)₂)₂, and SiH₃(N(CH₃)₂) in combination withammonia or nitrogen were also suggested as reactants. It was alsodisclosed that plasma produced by radiating the gas with an ultra-violetbeam, the temperature was decreased to 300° C.

U.S. Pat. No. 5,874,368 teaches the use of bis(tertiarybutylamino)silaneas a precursor to deposit silicon nitride using low pressure chemicalvapor deposition at a temperature range of 500° to 800° C.

U.S. Pat. No. 5,874,368 and U.S. Pat. No. 6,153,261 disclose theformation of silicon nitride films using bis(tertiarybutylamino)silaneas a silicon reactant gas. LPCVD is used to generate the film.

U.S. Pat. No. 6,391,803 discloses the formation of silicon containingthin films by atomic layer deposition using a silane of the formulaSi(N(CH₃)₂)₄, SiH(N(CH₃)₂)₃ SiH₂(N(CH₃)₂)₂ SiH₃(N(CH₃)₂), preferablytrisdimethylaminosilane, as a first reactant. A portion of the firstreactant is chemisorbed onto the substrate and a second portion isphysisorbed onto the substrate. The reactant is purged and a secondreactant, i.e., NH₃ is introduced.

BRIEF SUMMARY OF THE INVENTION

Classes of liquid aminosilanes have been found which allow for theproduction of silicon carbo-nitride films of the general formulaSi_(x)C_(y)N_(z) by CVD processes. These aminosilanes, in contrast tosome of the precursors employed heretofore, are liquid at roomtemperature and pressure and allow for convenient handling. In addition,the invention relates to a deposition process for producing such films.

The classes of compounds are generally represented by the formulas:

and mixtures thereof, wherein R is selected from C₁-C₁₀ alkyl groups,linear, branched, or cyclic, saturated or unsaturated; aromatic,heterocyclic, or silyl in formula C, R¹ is selected from C₂-C₁₀ alkylgroups, linear, branched, or cyclic, saturated or unsaturated; aromatic,heterocyclic, hydrogen, silyl groups with or without substituents with Rand R¹ in formula A also being combinable into a cyclic group (CH₂)_(n),wherein n is from 1-6, preferably 4 and 5 and R² representing a singlebond, (CH₂)_(n) chain, a ring, SiR₂, or SiH₂. Preferred compounds aresuch that both R and R¹ have at least 2 carbon atoms. The classes ofcompounds are generally represented by the formulas:

and mixtures thereof, wherein R and R¹ in the formulas representaliphatic groups typically having from 2 to about 10 carbon atoms, e.g.,alkyl, cycloalkyl with R and R¹ in formula A also being combinable intoa cyclic group, and R² representing a single bond, (CH₂)_(n), a ring, orSiH₂.

The precursors employed in CVD processes can achieve many advantages,and these include:

an ability to facilitate formation of dielectric films at low thermalconditions without incurring the problems of plasma deposition;

an ability to mix the aminosilanes with other precursors, e.g., ammoniaat various stoichiometries, for permitting control of the ratio of Si—Cbonds to Si—N bonds and thereby control the characteristics of theresulting films;

an ability to produce films having high refractive indices and filmstresses;

an ability to produce films having low acid etch rates;

an ability to produce films of high densities;

an ability to generate films while avoiding chlorine contamination; and,

an ability to operate at low pressures (20 mTorr to 2 Torr) in amanufacturable batch furnace (100 wafers or more); and,

an ability to generate Si_(x)C_(y)N_(z) films at low temperatures, e.g.,as low as 550° C. and below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of the stress values for films formed by the depositionof diethylaminosilane and bis(tertiary)butylamino)silane as a functionof the mole ratio of NH₃ to precursor in the deposition process.

FIG. 2 is a plot of the hardness of films formed by the deposition ofdiethylaminosilane and bis(tertiary)butylaminosilane as a function ofthe temperature in the deposition process against a standard SiO₂.

FIG. 3 is a plot of the infrared spectra ion of films generated by thedeposition of diethylaminosilane (neat), diethylaminosilane with NH₃ andbis(tertiary)butylamino)silane.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that classes of liquid organo aminosilanes having anN—SiH₃ group as a key feature in the molecular structure are suitable asprecursors for producing silicon carbo-nitride films via CVD in theelectronics industry. These compounds lend themselves to the productionof Si_(x)C_(y)N_(z) films under a variety of conditions.

The compounds herein are liquid at atmospheric pressure and roomtemperature, i.e., 25° C. and thus provide a significant advantage overthe reported usage of the trimethyl substituted aminosilane. They aresubstituted with organo groups having at least 2 carbon atoms in thechain on the amino group providing for stability under conventionalhandling and processing conditions.

One class of amino silane is resented by formula A as follows:

In this class of compounds R is selected from C₁-C₁₀ alkyl groups,linear, branched, or cyclic, saturated or unsaturated; aromatic,heterocyclic. R¹ is selected from C₂-C₁₀ alkyl groups, linear, branched,or cyclic, saturated or unsaturated; aromatic, heterocyclic, hydrogen,silyl groups, with or without substituents, and R and R¹ also beingcombinable into a cyclic group. Representative substituents are alkylgroups and particularly the C₂₋₄ alkyl groups, such as ethyl, propyl andbutyl, including their isomeric forms, cyclic groups such ascyclopropyl, cyclopentyl, and cyclohexyl. Illustrative of some of thepreferred compounds within this class are represented by the formulas:

where n is 1-6, preferably 4 or 5.

The second class of aminosilane has two silyl groups pendant from asingle nitrogen atom as represented by formula B.

As with the R groups of the Class A compounds, R is selected from C₂-C₁₀alkyl groups, linear, branched, or cyclic, saturated or unsaturated;aromatic, heterocyclic. Specific R groups include methyl, ethyl, propyl,allyl, and butyl; and cyclic groups such as cyclopropyl, cyclopentyl,and cyclohexyl. Illustrative compounds are represented by the formulas:

The third class of aminosilane compound is represented by formula C.These are generally diaminodisilyl compounds with R is same as R and R¹in formulas A and the R² group bridging the nitrogen atoms. Sometimesthe R² group is nothing more than a single bond between the nitrogenatoms or it may be a bridging group, such as SiR₂, SiH₂, a chain, or aring. The formula is as follows:

Specific examples include those represented by the formulas:

These compounds are synthesized in general by the following reactions,which are also demonstrated by Examples 1, 2, 3, and 4.

Although the above series of reactions illustrate a route to theaminosilanes as described, other sources of a silane precursor may beused. This route allows for a rather straight forward control as towhether mono and disilyl compounds are produced using the reactionstoichiometry and the use of a wide variety of amines.

Some of these compounds can also be synthesized by the reaction ofmonohalosilanes with corresponding amines, as described in ThePreparation and Properties of Dimethylamino and Diethylamino Silane[Aylett and Emsley, J. Chem. Soc. (A) p 652-655, 1967].XSiH₃+2RR¹NH→RR¹N—SiH₃+RR¹NH.HX

Representative amines well suited for the reaction are the alkyl,cyclic, and heterocyclic. Preferred amines are the lower alkyl amines,e.g., ethyl, iso-propyl, t-butyl, and cyclohexyl. Further the amines maybe primary or secondary depending upon the product desired.

In the formation of silicon carbo-nitride films, the mono ordiaminosilanes, optionally with ammonia or nitrogen source, are allowedto react in a deposition chamber at conventional depositiontemperatures. Such films may be formed in deposition chambers designedfor chemical vapor deposition (CVD), low pressure chemical vapordeposition (LPCVD) plasma enhanced CVD (PECVD), atomic layer deposition(ALD), and so forth. The term CVD as used herein is intended to includeeach of these processes which are employed in semiconductor deposition.

As stated in the advantages, the liquid aminosilanes described herein,in many cases offer the fabricator the ability to form siliconcarbo-nitride films via CVD at relatively low temperatures, although ageneral temperature range is from 500 to 700° C. Unexpectedly,Si_(x)C_(y)N_(z) film deposition can be achieved presumably because ofthe high activity of the SiH₃ group(s). It is believed the low sterichindrance for the ammonia transamination reaction on the silicon center,allows these compounds to react with ammonia and deposit films withincreasing nitrogen concentrations at relatively low temperatures.

The deposition of the aminosilane precursors may be carried out in theabsence of, or in the presence of, an active nitrogen source such ashydrazine, dimethylhydrazine, or ammonia. Molar ratios of the nitrogensource to aminosilane generally are broadly within the range of from 0:to >10:1. The upper limit is restricted by the dilution effect on theprecursor and the dilution effect will significantly diminish thedeposition rate. Preferred ranges are from 0.1 to 4:1. The formation offilms via deposition may also be carried out with or without other gasesincluding with inert gases, such as nitrogen and helium. The use ofgases by the fabricator to achieve corresponding dilution of theprecursor may improve the conformality of the deposition or improve thepenetration for chemical vapor infiltration.

Low pressure chemical vapor deposition processes (LPCVD) involvechemical reactions that are allowed to take place on a variety ofsubstrates, e.g., silicon, within a pressure range of 20 mTorr to 20Torr. High pressure CVD may result in gas phase nucleation orpredeposition before the desired substrate is reached. Dilution of theaminosilane precursor may be required for such high pressure reactions.Low pressure deposition with some of the aminosilane precursors mayexhibit rates of deposition to non-commercially usable levels. However,such aminosilanes may be suitable for atomic layer deposition.

In carrying out deposition processes, the aminosilanes described hereincan be blended with other silyl precursors to alter film properties.Examples of other precursors include bis-tert-butylaminosilane,tris-iso-propylaminosilane, bis-diethylaminosilane,tris-dimethylaminosilane, and bis-iso-propylaminosilane.

The following examples are intended to illustrate various embodiments ofthe invention including the synthesis of various silanes and the LPCVDof silicon carbo nitride film forming precursors.

Example 1 Synthesis of Diethylaminosilane

50 grams (0.33 mol) of trifluoromethanesulfonic acid and 100 ml oftoluene were added to a 250 ml flask. Under the protection of nitrogen,the flask was cooled to −40° C. 40.6 grams (0.33 mol) of tolylsilane wasadded slowly. Then the flask was cooled to −60° C. 33.5 grams oftriethylamine was added slowly, followed by addition of 24 grams ofdiethylamine. After addition, the temperature of the flask was allowedto warm to room temperature gradually. Two layers of liquid were formed.The upper layer was separated using a separation funnel. 25 grams ofdiethylaminolsilane was obtained by vacuum distillation. The boilingpoint of the diethylaminolsilane was 40-42° C. at 210 mmHg.

Example 2 Synthesis of Di-Iso-Propylaminosilane

50 grams (0.33 mol) of trifluoromethanesulfonic acid and 80 ml ofpentane were added to a 250 ml flask. Under the protection of nitrogen,the flask was cooled to −40° C. 35.6 grams (0.33 mol) of phenylsilanewas added slowly. Then the flask was cooled to −60° C. 33.3 grams (0.33mol) of triethylamine was added slowly, followed by addition of asolution 33.3 grams (0.33 mol) of di-iso-propylamine in 15 ml ofpentane. After addition, the temperature of the flask was allowed towarm to room temperature gradually. Two layers of liquid were formed.The upper layer was separated using a separation funnel. The solvent andby product benzene were removed by distillation. 30 grams ofdi-iso-propylaminosilane was obtained by vacuum distillation. Theboiling point of the di-iso-propylaminosilane was 55° C. at 106 mmHg.

Example 3 Synthesis of Cyclohexyldisilylamine and2,4-Dicyclohexyl-2,4-Diaza-1,3,5-Trisilapentane

62.5 grams of trifluoromethanesulfonic acid and 100 ml of pentane wereadded to a 500 ml flask. Under the protection of nitrogen, the flask wascooled to −40° C. 45 grams of phenylsilane was added slowly. Then theflask was cooled to −60° C. 42 grams of triethylamine was added slowly,followed by addition of a solution 20.6 grams of cyclohexylamine in 15ml of pentane. After addition, the temperature of the flask was allowedto warm to room temperature gradually. Two layers of liquid were formed.The upper layer was separated using a separation funnel. The solvent andby product benzene were removed by distillation. 15 grams ofcyclohexyldisilylamine was obtained by vacuum distillation. The boilingpoint of the cyclohexyldisilylamine was 54-55° C. at 17 mmHg. Theremaining high boiling point portion contains 96.6%2,4-dicyclohexyl-2,4-diaza-1,3,5-trisilapentane.

Example 4 Synthesis of Cyclohexyldisilylamine and2,4-Di-Tert-Butyl-2,4-Diaza-1,3,5-Trisilapentane

50.0 grams (0.33 mol) of trifluoromethanesulfonic acid and 100 ml ofpentane were added to a 500 ml flask. Under the protection of nitrogen,the flask was cooled to −40° C. 35.6 grams (0.33 mol) of phenylsilanewas added slowly. Then the flask was cooled to −60° C. 33.3 grams (0.33mol) of triethylamine was added slowly, followed by addition of asolution 28.7 grams (0.165 mol) of bis-t-butylaminosilane in 15 ml ofpentane. After addition, the temperature of the flask was allowed towarm to room temperature gradually. Two layers of liquid were formed.The upper layer was separated using a separation funnel. The solvent andby product benzene were removed by distillation. 21 grams of2,4-di-tert-butyl-2,4-diaza-1,3,5-trisilapentane was obtained by vacuumdistillation.

Example 5 Formation of Silicon Carbo Nitride Film UsingDiethylaminosilane Precursor

General Procedure

The aminosilane precursors are tested in an LPCVD reactor used toqualify experimental precursors for silicon carbo-nitride depositions.The precursors are degassed and metered into the reactor through alow-pressure mass flow controller (MFC) as required. The MFC flows arecalibrated against weight losses of the chemicals vs. time of flow.Additional reactants, such as ammonia, and diluents, such as nitrogenand helium, as specified are also metered into the reactor throughcalibrated MFCs, as required. The reactor is connected to a rootsblower/dry pump combination capable of evacuating the reactor to below10⁻⁴ Torr (0.013 Pa). The temperature across a load of silicon wafers,during deposition, is within 1° C. of the set point.

Silicon wafers are loaded onto a quartz boat and inserted in thereactor. The reactor is pumped to base pressure and checked for leaks.The system is ramped to the process temperature with gas flows thatwould dilute any residual oxygen or moisture to prevent any oxidation ofthe silicon wafers as the reactor heats up. The reactor is thenstabilized for a predetermined time to bring all wafer surfaces to anequal temperature (as had been determined by previous measurements onwafers with attached thermocouples).

The gases and vapors are injected into the reactor for a predetermineddeposition time at a controlled pressure. Next, the gases are shut off,and the reactor is pumped to a base pressure. The reactor, then, ispump-purged, pumped down, and pump-purged to clear any reactive gases orvapors as the reactor is cooled down. The reactor is backfilled toatmospheric pressure; the wafers are removed and allowed to cool to roomtemperature. The deposited films are then measured for film thickness,film refractive index, film stress (FIG. 1), infrared absorbances (shownin FIG. 3), dielectric constant, and acid etch rate (Table 1).

In forming the deposited films, 10 sccm of diethylaminosilane (DEAS) wasflowed into a reactor at 570° C. along with 20 sccm NH₃ and 20 sccm N₂at 1.3 Torr (173.3 Pa) for a deposition time of 60 minutes.

The average film thickness was 69 nm and refractive index was 2.045. Thefilm stress was measured as 1.07×10¹⁰ dynes/cm² (1.07 GPa).

The infrared spectra were dominated by Si—C and Si—N absorptions. C—H orC—N absorptions were in the noise illustrating, as shown in FIG. 3, thefilm composition was largely in the form of Si_(x)C_(y)N_(z) as isdesired.

Example 6 Formation of Silicon Carbo-Nitride Film UsingDiethylaminosilane Precursor Using N₂ without NH₃

The procedure of Example 4 was followed with the exception of processconditions. Nitrogen was used in place of NH₃. In this example, 10 sccmof diethylaminosilane (DEAS) was flowed into a reactor at 600° C. with40 sccm N₂ at 1.0 Torr (133 Pa) for a deposition time of 40 minutes.

The average film thickness was 42 nm and refractive index was 2.288. Thefilm stress was measured as 1.34×10¹⁰ dynes/cm². These films have evenhigher stresses and lower etch rates than those obtained with ammonia(See Table 1 for etch rates). The conformalities of such films werefound to be 100% on isolated structures.

Example 7 Formation of Silicon Carbo-Nitride Film UsingDiisopropylaminosilane Precursor Using N₂ without Nh₃

The procedure of Example 5 was followed with the exception of theprecursor. 10 sccm of diisopropylaminosilane (DIPAS) was flowed into areactor at 570° C. with 20 sccm He and 20 sccm N₂ at 1.0 Torr (133 Pa)for a deposition time of 70 minutes.

The average film thickness was 46 nm and refractive index was 2.056. Thefilm stress was measured as 1.07×10¹⁰ dynes/cm². Surprisingly, therefractive index and stress were similar for diisopropylaminosilane tothat of the precursor of Example 6. These results show excellent stressvalues within this class of materials can be achieved.

Example 8 Formation of Silicon Carbo-Nitride Film Using Bis(TertiaryButylamino)Silane Precursor as a Control Using N₂ without NH₃

The procedure of Example 5 was followed with the exception of theprecursor and it was used as a control. BTBAS is a precursor used inproduction processes worldwide and it was chosen as the representativeaminosilane comparison because of its well accepted performancecharacteristics.

10 sccm of bis(tertiary butylaminosilane) (BTBAS) was flowed into areactor at 570° C. with 20 sccm He and 20 sccm N₂ at 1.0 Torr (133 Pa)for a deposition time of 70 minutes. These films have only 20% of thestress and less than 10% of the etch resistance of the mono-aminosilanes(See Table 1).

FIG. 1 was generated using the stress data with respect to bis(tertiarybutylaminosilane) and diethylaminosilane. It shows the results of stressmeasurements using an FSM system. The results for diethylaminosilanewere unexpected, i.e., a high stress at a low NH₃:DEAS ratio wasachieved including that of maintaining a high stress modest NH₃:DEASratios.

Precursors such as bis(tertiarybutylamino)silane and dichlorosilaneproduce films that have decreasing stresses as the ammonia to chemicalratio is decreased. At a low NH₃:BTBAS ratio stress results are poor.Reducing the ammonia for these precursors creates a silicon rich filmand this reduces the thermal expansion coefficients of these filmsrelative to the silicon substrate. Although not intending to be bound bytheory, reducing the ammonia:DEAS ratio in the deposition processincreases the Si to N atomic ratio, the effect is that the C to Siatomic ratio increases. Apparently, then, there is some replacement ofSi—N with Si—C bonds and these bonds result in producing films havingsimilar stress.

A second component of the example was the measurement of film hardness.It was measured by indentation using a Hysitron system. FIG. 2 is a plotwhich shows the deposited film hardness. When diethylaminosilane wasused as the precursor as compared to a BTBAS deposition and to thermallygrown silicon dioxide harder films were obtained. Harder films are moreprotective of underlying layers and themselves in chemical-mechanicalpolishing (CMP) operations. This property, too, was surprising.

Example 9 Etch Resistance of Silicon Nitride and Silicon Carbo-NitrideFilms

In this example, the results of etching of various silicon nitride andsilicon carbo-nitride films are set forth in Table 1. Table 1 displaysthe results of etching films from several precursors in 1% (of 49%) HF.The etch rates are given relative to those of thermally grown silicondioxide that were etched at the same time. The lower the etch rate of afilm, the better it is for maintaining geometries and protectingunderlying layers as undesired silicon dioxide is removed.

TABLE 1 Comparison of film etch rates in 1% of 49% HF at 24° C. 1% HFEtch Deposition Rate NH₃ Temperature, Relative Chemical ratio ° C. toSiO₂ BTBAS 2:1 570 0.188 BTBAS 0 570 0.018 DEAS 2:1 570 0.006 DEAS 4:1570 0.008 DEAS 1:1 570 0.009 DEAS 0 570 0.001 DIPAS 2:1 570 0.006 DIPAS0 570 0.006 BTBAS = bis(tertiarybutylamino)silane DEAS =diethylaminosilane DIPAS = diisopropylaminosilane

From the above Table 1, DEAS is shown to have excellent low etch ratesat NH₃ to precursor ratios of from 0 to 2. On the other hand, a ratio ofNH₃:BTBAS, even at an NH₃:BTBAS ratio of 0:1:1 gave higher etch rates,than DEAS at a 2:1 ratio. Excellent low etch rates are shown at lowNH₃:BTBAS ratios, but recall with BTBAS stress levels are poor at thelow NH₃:BTBAS level.

Summarizing, dielectric silicon carbo-nitride films of the formula,Si_(x)C_(y)N_(z), can be produced from the classes of aminosilanes asdescribed, by CVD and other deposition processes. It is believed thehigh activity of the SiH₃ group allows for the production ofSi_(x)C_(y)N_(z) film depositions at temperatures as low as 550° C.whereas many of the precursors for forming Si_(x)C_(y)N_(z) films do notperform well.

It is believed, also, the low steric hindrance for the ammoniatransamination reaction on the silicon center allows these compounds toreact with ammonia and form films with increasing nitrogenconcentrations at relatively low temperatures. Ligands such as ethyl,isopropyl, butyl, etc. act as good leaving groups as they becomevolatile byproducts by beta-hydride elimination. Any carbon left behindis bonded to silicon. In contrast, aminosilane precursors which havemethyl groups as reported in the past do not have this dissociationroute. They remain bonded to the nitrogen and can be incorporated andtrapped in the growing film. The presence of such trapped methyl groupsare easily distinguished in infrared spectra (see FIG. 3). Here, though,the absence of a C—H peak in FIG. 3 indicates that there can be only bea very low level of hydrocarbon trapped in the film.

1. A composition for depositing a dielectric film comprising: anaminosilane comprising the following formula A:

wherein R and R¹ are each independently selected from the groupconsisting of isopropyl, t-butyl, sec-butyl, t-pentyl, sec-pentyl,cyclopropyl, cyclopentyl, and cyclohexyl groups; and optionally aprecursor selected from the group consisting ofbis-tert-butylaminosilane, tris-iso-propylaminosilane,bis-diethylaminosilane, tris-dimethylaminosilane, andbis-iso-propylaminosilane wherein R and R¹ in formula A are optionallycombined into a cyclic group.
 2. The composition of claim 1 wherein Rand R¹ are combined into a cyclic group.
 3. The composition of claim 1wherein R and R¹ are isopropyl groups.
 4. The composition of claim 1wherein the precursor comprises bis-tert-butylaminosilane.
 5. Thecomposition of claim 1 wherein the precursor comprisestris-iso-propylaminosilane.
 6. The composition of claim 1 wherein theprecursor comprises bis-diethylaminosilane.
 7. The composition of claim1 wherein the precursor comprises tris-dimethylaminosilane.
 8. Thecomposition of claim 1 wherein the precursor comprisesbis-iso-propylaminosilane.
 9. A composition for depositing a dielectricfilm comprising: an aminosilane comprising the following formula A:

wherein R and R¹ are each sec-butyl groups; and optionally a precursorselected from the group consisting of bis-tert-butylaminosilane,tris-iso-propylaminosilane, bis-diethylaminosilane,tris-dimethylaminosilane, and bis-iso-propylaminosilane.
 10. Thecomposition of claim 2 wherein R comprises isopropyl and R¹ comprisessec-butyl.